1. Field of the Invention
This invention relates to a gel electrolyte battery having a gel electrolyte.
2. Description of Related Art
As a power source for a portable electronic equipment, such as a portable telephone set, a video camera or a notebook personal computer, the importance attached to batteries is increasing. For reducing the size and weight of the electronic equipment, such a battery is desired which not only is of a large capacity but also is lightweight and space-saving. Viewed in this light, a lithium battery, having a high energy density and high output density, is suited very much. A lithium battery, employing a carbon material as a negative electrode material, has an average discharge voltage of not lower than 3.7 V and undergoes lesser cyclic deterioration during charging/discharging, so that it has a merit that a high energy density can readily be realized.
The lithium battery is desired to exhibit flexibility and shape freedom, and lithium batteries of various shapes, such as a sheet battery of thin thickness and large area, or a card battery of a thin thickness and a small area, are also desired. However, in the conventional technique of enclosing a battery device comprised of positive and negative electrodes and an electrolytic solution within an exterior metallic can, it is difficult to fabricate batteries of variable shapes such as those depicted above. Moreover, the use of the electrolytic solution tends to complicate the manufacturing process or renders it necessary to provide leakage-resistant means.
For overcoming the above-mentioned problems, such battery is being envisaged which uses a solid electrolyte employing an electrically conductive organic high polymer material or organic ceramics, or a gelated solid electrolyte having an electrolytic solution impregnated into a matrix polymer, referred to below as a gel electrolyte. With the solid electrolyte battery, employing the solid electrolyte, or with the gel electrolyte battery, employing the gel electrolyte, in which the electrolyte is immobilized, it is possible to fabricate the battery using a film-shaped exterior material to a reduced thickness, thus providing a higher energy density than is possible with the conventional battery.
However, the gel electrolyte battery has a deficiency that, since the electrolytic solution is held in the matrix polymer, the electrolytic solution cannot sufficiently seep into the layer of the active materials of the electrodes. As a result, lithium ions cannot be migrated sufficiently across the electrodes, with the result that a desired battery capacity cannot be achieved.
Moreover, in a gel electrolyte battery, the solvent in the gel electrolyte tends to be decomposed at the time of activation charging to evolve gases, with the result that local gaps are produced between the layer of the active material and the gel electrolyte to impair the adhesion between the layers of the active materials of the electrodes and the gel electrolyte. If such gap is produced between the layer of the active material and the gel electrolyte, the battery in storage is deteriorated appreciably in battery voltage to prove a reject to lower the production yield. Moreover, lithium ion migration across the electrodes is retarded to render it extremely difficult to realize the desired battery capacity.